This invention generally relates to a vascular access system for locating structures such as blood vessels within a patient's body. More specifically, this invention relates to a flexible coaxial cable probe for locating body structures within a patient using Doppler technology that provides a relatively adjustable length so that it is adaptable to a variety of needles.
The insertion of arterial and venous catheters for various purposes including angiography can prove difficult for medical professionals. Locating and penetrating arteries and veins is especially difficult when dealing with patients who are obese or present unusual anatomy. When a medical professional has difficulty locating an artery or vein, the patient is subjected to increased discomfort. Various devices improve accuracy in locating vessels within a patient's body and, thereby decrease the amount of discomfort a patient must endure. One such attempt includes the use of Doppler ultrasound technology.
The potential utility of Doppler ultrasound for accurately guiding a needle into a vessel has been recognized. Certain applications utilize the transmission of ultrasonic waves through the needle and the reception of ultrasonic echoes by a separate transducer located on the body of the patient separated from the syringe an needle. Such applications can give erroneous signals, particularly when the needle is engaging the blood vessel or immediately before penetrating the blood vessel. An improvement over such applications includes a transducer insert positioned within a hollow needle that has an ultrasonic transducer at one end for transmitting and receiving ultrasonic waves within the sharpened end of the needle. However, the fixed construction of the latter transducers typically limits their application to a specific size (length) of needle.
When the transducer probe has a rigid body for a portion of its length, this rigid body portion is typically located within the needle and a portion of a needle housing. A typical needle housing for a probe of this type includes a side arm through which the transducer is electrically coupled to a power source and/or a device for interpreting information gained through the transducer. Such side arms are typically oriented at an acute angle bend relative to the axis of the needle. Because the probe body is rigid, it cannot be retracted around the bend and back through the side arm. Thus, a coaxial cable has been connected to the rigid body probe to properly electrically couple the transducer to the power source. The coaxial cable is used for its ability to be bent at the turn between the longitudinal axis of the needle housing and the side arm. However, the cable attachment to the rigid body probe necessarily includes a larger diameter due to the soldering and shrink tubing needed to make the connection. This larger diameter connection prohibits the probe from advancing down into the needle while the rigidity of the probe body in the needle does not allow the probe to retract into the side arm. Therefore, such probes inherently have a fixed length relative to the needle and/or needle housing.
Nevertheless, it is desirable to have a transducer probe for utilizing Doppler ultrasound techniques that has a relatively adjustable length within a needle and needle housing. When a probe has a fixed length relative to a needle, the number of needles that can be used with such a probe is normally limited to one. This is because the location of the probe near the distal end of the needle is crucial to proper functioning and use of Doppler ultrasound techniques. Thus, a probe having a relatively adjustable length would have the advantage of being adaptable to a variety of needle sizes (lengths). Further, such a probe inherently would provide cost efficiencies as it is usable with a variety of needles for a variety of applications.